Pamidronic Acid → Sodium (3-amino-1-hydroxy-1-phosphonopropyl)phosphonate

32.7 g of 3-amino-1-hydroxypropane-1,1-diphosphonic acid are suspended in 106 ml of demineralised water. The suspension is heated to 35° and, while stirring vigorously, 28 ml of 30% aqueous sodium hydroxide solution are added dropwise at such a rate that the temperature of the reaction mixture rises to 54°. A clear solution is obtained initially from which crystallisation begins immediately. The whole is allowed to cool slowly to room temperature while stirring is continued, and then stirred for 8 hours at room temperature, filtered with suction, washed with a mixture of 2 parts by volume of methanol and 1 part by volume of water and dried at 30° under approximately 20 mbar until the weight is constant. Disodium 3-amino-1-hydroxypropane-1,1-diphosphonate is obtained in the novel crystal form containing water of crystallisation (modification E), the IR spectrum of which is identical to that of the product obtained according to Example 1.